1. Field of the Invention
This invention relates to telephoto zoom lenses, and more particularly, to telephoto zoom lenses having a range of magnification of about 3 with a minimized bulk and size.
2. Description of the Prior Art
In the past, the telephoto type has found its use in many zoom lenses. For example, the zoom lenses proposed in U.S. Pat. Nos. 4,223,981, 4,240,699 and 4,350,416 and Japanese Laid-Open Patents Application No. Sho 51-37247, 51-63635, 52-56946 and 53-131852 are generally constructed in the form of four lens components, or, from front to rear, a 1st component which is held stationary during zooming and is axially movable for focusing, a 2nd component which axially moves to change the focal length of the entire lens system, a 3rd component which axially moves in differential relation to the 2nd component so as to maintain the constant position of the image plane, and a 4th component which is held stationary during zooming and is composed of an image forming lens group in the rear of the aforesaid 1st to 3rd components to satisfy a desired focal length and position of the image point.
Of the zoom lenses of such configuration, those which have an image angle range beginning with 33.degree.-38.degree. for the wide angle positions and a zoom ratio of about 3 upon consideration of the degree of minimization of the bulk and size of the lens system in terms of the ratio of the total length (distance from the front vertex to the image plane) to the focal length, or the telephoto ratio, were taken at a value of as large as unity, and even in the shortest ones, at about 0.9.
In this manner, the conventional zoom lens, because the 1st lens component performing only the focusing function and made stationary during zooming and because it takes the form that the total length of the lens system is maintained constant as the focal length varies from the wide angle side to the telephoto side, tends to become relatively longer in the longitudinal direction.
On the other hand, there have been proposed a zoom lens having the 1st component made movable to change the image magnification as, for example, disclosed in U.S. Pat. No. 4,232,942 and Japanese Laid-Open Patent Application No. Sho 53-142251 and Japanese Patent Publication No. Sho 4923911. But, because these known zoom lenses are of the optically compensated type and since it is necessary that the shift of the image plane due to zooming as an error may fall within the depth of field, the total movement of the zoom components is unavoidably increased, and a valuable increase in the zoom ratio is difficult to achieve. Therefore, the conventional zoom types are not suited for a high-range, small-sized zoom lens.